Prior art wire fence strectching tools generally required that a hand would have to be kept around the relatively pivoted members of the tool to keep it engaged on a fence wire making it awkward to nail the wire to the fence post with just the other hand. Basically, in the prior art the members were rather loosely pivoted to avoid wear. Because of this loose pivoting the fence wire would not wedge itself between the jaws carried by the member in a manner to frictionally maintain the jaws closed.
If the danger of wear could be eliminated, it would be possible to pivot the members tightly in a manner that the tool could retain itself clamped about a fence wire. Then only the body need be leaned against the tool to keep the wire taught and both hands would be free for nailing.